Introduction to Particle Physics (for non physics students) 2. PARTICLES (from atoms to quarks and leptons) Structure of Matter
Two ways that structure is revealed:
True from atoms to particles….. Spectra
Qualitatively similar Spectra
Quantitatively different Scattering
Nuclear atom
Proton/neutron
Quarks
Qualitatively similar Rutherford: Nuclear Atom
Alpha particles from natural radioactivity
Gold leaf
Small scintillation screen Rutherford used energy conservation… …and long division ..and how Rutherford used them Quarks in the proton
Qualitatively: Same idea
Quantitatively: Different scale SLAC 3km electron accelerator
The BEAM Quarks in the proton
Electron beam = 3 km
Proton target (hydrogen)
Big electronic detector TARGET DETECTOR
BEAM me Proton made of 3 quarks, gripped by gluons To make proton and neutron requires two “flavours” of Quarks
Up and down Quarks and neutron ddu H atom (not to scale!) a miracle of neutrality electron balances uud hint of unification
beta decay at quark level
Stars cook the elements
Sun is dominantly this first step
Heavy elements cooked in stars and ejected into cosmos in supernova explosion
Many protons; electrical disruption Stabilised by STRONG force
How do we know the neutrino is produced?
It hits a nucleus upstream and turns into charged lepton which is detected.
Three charged leptons electron muon tau And three neutral: e-neutrino mu-neutrino tau-neutrino
Neutrinos and their e-neutrino electron charged partner mu-neutrino muon are always linked tau-neutrino tau if neutrinos are massless BUT if neutrinos have mass, they can oscillate back and forth
Neutrino Oscillations
• Nu beams from lab (CERN,Fermilab,KEK) • Measure intensity nearby • Measure 100s km away
• Evidence that nu are disappearing • Direct evidence for oscillation not yet
• Major research programme to understand neutrinos- masses, mixing, key to pattern of the three generations?
• Muon-neutrino Nature’s Three Party System Spectra
So are quarks (and leptons) also composites? MATTER quarks electron neutrino leptons
ANTIMATTER antiquarks ANTIMATTER positron antineutrino antileptons MATTER qqq proton
ANTIMATTER ANTIMATTER qqq antiproton leptons MATTER qqq proton BARYONS
q MESONS q
ANTIMATTER qqq antiproton ANTIBARYONS A Very Short Introduction Coming out in December NEW More in Vsi
And particle odyssey The Particle Odyssey TheA Journey Particle to the Heart Odyssey of matter
Frank Close, Michael Marten, Christine Sutton